1. Field of the Invention
The invention applies to the class of devices which convert the information contained in frequency modulated, phase modulated or amplitude modulated electromagnetic signals and the like generated by a variety of detectors into a visible image.
2. Description of the Prior Art
The classic device for performing the function outlined above is a cathode ray tube. This device produces light fairly economically with respect to power input and operates to high levels of luminance and resolution. The tube itself, however, is bulky and heavy making it difficult to accommodate in small systems such as head mounted displays or in limited spaces like aircraft cockpits. There are also problems in data systems with the various types of distortion to which focussed electron beams are suspectible.
Most of the above problems are allieviated by using a solid state flat panel display. The picture elements (pixels) that provide final resolution of the image are defined by electrodes or by the size and shape of each light emitting element. These displays can also be composed of externally illuminated reflecting elements as found in liquid crystal arrangements. This requirement, however, sometimes conflicts with military needs for a low level of ambient luminance to prevent detection by the enemy. Thin film electroluminescent devices work very well in these displays but have a very limited brightness, e.g. 350-500 NITS, which makes them difficult to read against high ambient light levels. Light emitting diodes are better in this respect, but are inefficient and difficult to fabricate in useful sizes and shapes for this purpose, which results in higher costs and compromises in the resolution of the display.